It is generally understood that there are advantages to a liquid preparation when making a bait for use with insects that prefer or even require their food to be in liquid form prior to ingestion or digestion. Commercially available liquid ant baits are familiar, such as the water and sucrose product sold under the name "Terro Ant Killer" by Senoret Chemical Co., Inc. of St. Louis, Mo. However, liquid and even moist baits tend to dry out when exposed to the air during use, losing their advantage.
Brenner et al., U.S. Pat. No. 4,988,510, address the general problem of drying. Brenner et al. disclose a semi-solid insect bait that includes one or more humectants formulated together with an attractant and an insecticide to create a deformable, hydrophilic gel matrix. Sugars, glycerol, and other polyhydroxy alcohols are cited as humectants useful in the bait for the purpose of drawing moisture from the air to allow the bait to remain pliable and relatively moist. The humectant is stated to be present in an "effective amount," which is defined as that amount necessary to achieve the intended result of the component. For humectants, Brenner et al. describe that amount as being 30-45%; on a dry weight basis.
The inclusion of sorbitol in an insect bait is relevant to the present invention, and the polyhydroxy alcohols, referred to as a class by Brenner et al., could include sorbitol. Furthermore, Hagerty, U.S. Pat. No. 4,889,710, and Inazuka et al., U.S. Pat. No. 4,160,824, specifically include sorbitol in the insect bait preparations they describe. However, the Brenner et al. bait is not liquid, and Hagarty and Inazuka et al. utilize sorbitol not as a humectant but, instead, as an emulsifier. In Hagarty, an aerosol foam is disclosed that is formed of a water soluble, film-forming polymer. An emulsifier is included to emulsify the film-forming polymer so that it will foam, and sorbitol derivatives are cited among the examples of useful emulsifiers. Emulsifier amounts in the Hagarty composition range from 0.01 to 5% by weight.
Inazuka et al. describe insect attractive compositions that, among other options, may be used in solutions or emulsions, if dissolved or dispersed in a suitable liquid carrier with the aid of an emulsifier, dispersing agent, or the like. Sorbitols are referred to generally as being among the suitable emulsifiers, spreading agents, and penetrants for use with the Inazuka et al. insect attractive compositions. The proposed amount of sorbitol is not specified, and one skilled in the art therefore would understand that a conventional or an effective amount is being referred to. The disclosure of Hagarty, cited above, shows that one skilled in the art would expect such emulsifiers to be effective in an amount between 0.01 to 5% by weight.
Sorbitol is a commercially available material and is on the market as an aqueous solution in a variety of concentrations for a variety of purposes. Thus, sorbitol is conventionally available for manufacturing and other purposes in an aqueous solution that is approximately 70% sorbitol by weight. Gerber et al., U.S. Pat. No. 2,829,085, is a further example of sorbitol solutions in concentrations relevant to the present invention. Gerber et al. describe a parenteral vehicle for therapeutic agents in which sorbitol is used to aid in the suspension of non-soluble therapeutic agents in injectable aqueous preparations. In Gerber et al., sorbitol is used in an amount sufficient to raise the specific gravity of the water solution in which it is dissolved until it is substantially equal to the specific gravity of the therapeutic agent that is be suspended within the injectable preparation. Weight percentages of 30.4% and 59.2% are cited in two examples given to show the application of the Gerber et al. invention to two different therapeutics.
Neither Hagarty, Inazuka et al., nor Gerber et al. utilize sorbitol for its humectant properties, nor are any of them concerned with strategies to delay the drying of their preparations.